It is known to adjust the flow cross-section of valves by simple restriction of the length of stroke, in order for example, to influence the speed of hydraulic loads such as hydraulic motors and operating cylinders. Such stroke limitation is manually and mechanically set by means of an adjustable stop abutment screw.
It is a disadvantage of this manner of adjustment that a plurality of main valves must be used to achieve two independently adjustable flow cross-sections, thus substantially increasing the cost of controls for hydraulic loads.
The prior art also discloses servo valves which can be used as regulating valves for the continuous adaptation of the flow cross-section and therefore of the speed of the appropriate electrical control. Owing to the large amount of electrical equipment and the need for satisfying special conditions regarding the filtering of the hydraulic fluid and because of maintenance requirements this method is too costly for simple control functions.